cf push: support pushing from saved container image tarball

What's the user value of this feature request?

Users can push a container image without having to publish to a container registry. This is useful for testing or containers that contain non-public information.

Who is the functionality for?

Anyone who wants to cf push containers without publishing to a container registry.

How often will this functionality be used by the user?

I would use it daily. I am not sure how often other users would use it.

Who else is affected by the change?

I do not believe this would cause any breakage. It would allow containers to be pushed from a saved container image tarball in addition to container registries.

Is your feature request related to a problem? Please describe.

I'm always frustrated when I have to setup a container registry just to cf push a container-based app.

Describe the solution you'd like

cf push APP-NAME --docker-saved-image my_saved_app_image.tar

Describe alternatives you've considered

No viable alternatives. Container images must be deployed from container registries. This means the container must be published to a public registry or you must setup your own container registry. This is not ideal for testing or containers that have non-public data.